为了研究Mg_(97)Gd_(2)Y_(1)合金中β'相的粗化过程以及相关析出结构的形成和演变机制,使用原子分辨的高角度环形暗场-扫描透射电子显微镜(high angle annular dark field scanning transmission electron microscope,HAADF-STEM)...为了研究Mg_(97)Gd_(2)Y_(1)合金中β'相的粗化过程以及相关析出结构的形成和演变机制,使用原子分辨的高角度环形暗场-扫描透射电子显微镜(high angle annular dark field scanning transmission electron microscope,HAADF-STEM)成像技术表征了合金不同时效阶段形成的析出结构,并结合第一性原理计算的方法分析了它们的稳定性.结果表明,相关的β_(F)'、β_(M)和β″相主要在β'相粗化过程的早期形成,它们的形成与β'相相界面周围存在较高的错配应变场密切相关;随着β'相粗化过程的进行,β_(M)和β″相的尺寸和数量逐渐减少,而由β'与β_(F)'相交替组成的竹节状析出物增多,成为合金基体中主要的析出结构;当错配应变足够大时,β_(F)'相内部出现位错,β相在位错处可以形核,并逐渐长大成为基体中主要的平衡析出结构.展开更多
采用聚焦离子束定点切割技术(Focused ion beam,FIB),透射电镜(Transmission electron microscopy,TEM)、高角度环形暗场扫描透射电镜(High angle annular dark field scanning transmission electron microscopy,HAADF-STEM)和扫描电镜...采用聚焦离子束定点切割技术(Focused ion beam,FIB),透射电镜(Transmission electron microscopy,TEM)、高角度环形暗场扫描透射电镜(High angle annular dark field scanning transmission electron microscopy,HAADF-STEM)和扫描电镜(Scanning electron microscopy,SEM)等技术手段,对Mg-7Gd-5Y-1Nd-2Zn-0.5Zr合金铸态及(515℃,48 h)均匀化态的组织形貌进行观察分析。结果表明:铸态合金晶界共晶组织中含有(Mg,Zn)_(3)RE相(FCC,a=0.72 nm)、Mg_(5)(RE,Zn)相(FCC,a=2.24 nm)及块状长周期堆垛有序(Long-period stacking ordered,LPSO)相。其中LPSO相主要为18R结构,存在少量14H结构,局部区域存在少量不完整周期的LPSO结构;此外合金中存在分布于共晶相附近的微米级富RE相以及分布于晶粒内部的微米级富Zr颗粒。经过(515℃,48 h)均匀化热处理,晶界(Mg,Zn)_(3)RE相和Mg_(5)(RE,Zn)相完全回溶,残留相主要为14H-LPSO相,局部区域存在具有不同晶体结构的LPSO过渡相。在铸态合金的晶粒内部,沿[1120]_(a)晶带轴观察,发现存在几个原子面至纳米尺度的LPSO构建块,由不同数量的LPSO构建块单元(4个RE/Zn原子层)及Mg原子层交替堆垛构成,RE/Zn与Mg原子层堆垛次序不具备完整周期性;均匀化热处理后,晶内的LPSO构建块几乎回溶,仅剩下极少量单个LPSO构建块单元。沿[0001]_(a)晶带轴观察,晶粒内部存在多种分布方式的富RE/Zn原子柱,为Mg-Gd-Y系镁合金时效过程β′析出序列中GP区的早期结构。展开更多
The effect of pre-straining on the structure and formation mechanism of precipitates in an Al−Mg−Si−Cu alloy was systematically investigated by atomic resolution high-angle annular dark-field scanning transmission ele...The effect of pre-straining on the structure and formation mechanism of precipitates in an Al−Mg−Si−Cu alloy was systematically investigated by atomic resolution high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM).Elongated and string-like precipitates are formed along the dislocations in the pre-strained Al−Mg−Si−Cu alloy.The precipitates formed along the dislocations exhibit three features:non-periodic atomic arrangement within the precipitate;Cu segregation occurring at the precipitate/α(Al)interface;different orientations presented in one individual precipitate.Four different formation mechanisms of these heterogeneous precipitates were proposed as follows:elongated precipitates are formed independently in the dislocation;string-like precipitates are formed directly along the dislocations;different precipitates encounter to form string-like precipitates;precipitates are connected by other phases or solute enrichment regions.These different formation mechanisms are responsible for forming different atomic structures and morphologies of precipitates.展开更多
A combinatorial approach was applied to investigating the influence of Fe content on the microstructures and properties of Ti6Al4V alloy.A diffusion couple was manufactured with Ti6Al4V and Ti6Al4V20Fe alloys and anne...A combinatorial approach was applied to investigating the influence of Fe content on the microstructures and properties of Ti6Al4V alloy.A diffusion couple was manufactured with Ti6Al4V and Ti6Al4V20Fe alloys and annealed at 1000°C for 600 h to obtain a wide range of compositions.By combining electron probe micro-analysis(EPMA),scanning electron microscopy(SEM)and nanoindentation,the relationships between composition and microstructure as well as hardness were determined.It is found that after aging the Ti6Al4V5Fe sample contains reasonable(about 55%)volume fraction of fineαphase and shows the peak hardness among the Ti6Al4VxFe alloys.Therefore,it is a promising candidate for the development of titanium alloys.HAADF-STEM and XRD reveal that after quenching from the singleβphase field,the metastableα''lamellae form in the Ti6Al4V5Fe alloy,and on subsequent isothermal aging,theα''lamellae become coarse and act as precursors/preferential nucleation sites for the stableαphase.展开更多
The morphology and crystal structure of the precipitates in Mg-7Gd-3Y-1Nd-1Zn-0.5Zr(wt.%)alloy with fine plate-like 14H-LPSO structures aged at 240℃were investigated using transmission electron microscopy(TEM)and hig...The morphology and crystal structure of the precipitates in Mg-7Gd-3Y-1Nd-1Zn-0.5Zr(wt.%)alloy with fine plate-like 14H-LPSO structures aged at 240℃were investigated using transmission electron microscopy(TEM)and high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM).Fine plate-like 14H-LPSO structures precipitate after heat treatment at 500℃for 2 h,andβ-type phases precipitate after the alloy is aged at 240℃.The long-period atomic stacking sequence of 14H-LPSO structures along the[0001]αdirection is ABABCACACACBABA.After being aged at 240℃for 2 h,theβ-type phases are the ordered solution clusters,zig-zag GP zones,and a small number ofβ′phases.The peak hardness is obtained at 240℃for 18 h with a Brinell hardness of 112,theβ-type phases areβ’phases and local RE-rich structures.After being aged at 240℃for 100 h,theβ-type phases areβ’,β1 andβ’F phases.β′phases nucleate from the zig-zag GP zones directly withoutβ″phases,and then transform intoβ1 phase byβ’→β’F→β1 transformations.The Zn not only can form LPSO structure,but also is the constituent element ofβ1 phases.LPSO structures have a certain hindrance to the coarsening ofβ’andβ1 along<0001>α.展开更多
Solid helium bubbles were directly observed in the helium ion implanted tungsten(W), by different transmission electron microscopy(TEM) techniques at room temperature. The diameters of these solid helium bubbles r...Solid helium bubbles were directly observed in the helium ion implanted tungsten(W), by different transmission electron microscopy(TEM) techniques at room temperature. The diameters of these solid helium bubbles range from1 nm to 8 nm in diameter with the mean bubble size about 3 nm. The selected area electron diffraction(SAED) and fast Fourier transform(FFT) images revealed that solid helium bubbles possess body-centered cubic(bcc) structure with a lattice constant of 0.447 nm. High-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)images further confirmed the existence of helium bubble in tungsten. The present findings provide an atomic level view of the microstructure evolution of helium in the materials, and revealed the existence of solid helium bubbles in materials.展开更多
本论文使用球差校正的高角环形暗场扫描透射电镜(Aberration-Corrected High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy,HAADF-STEM)结合选区电子衍射(Selected Area Electron Diffraction,SAED)技术系统表...本论文使用球差校正的高角环形暗场扫描透射电镜(Aberration-Corrected High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy,HAADF-STEM)结合选区电子衍射(Selected Area Electron Diffraction,SAED)技术系统表征了Mg-19.6 wt.%Gd合金300℃等温时效100 h后的时效析出行为。研究结果表明,Mg-19.6 Gd合金时效后期析出的平衡相为β-Mg5Gd。β-Mg5Gd相为fcc结构(空间群:■;晶格参数:a=22.34?),呈透镜状。β-Mg5Gd相具有一个■的惯习面,它们沿■3个方向均匀分布。β-Mg5Gd相在β1-Mg3Gd中形核,并由内而外生长取代β1相。β相与β1,以及与α-Mg基体都是完全共格的,其与β1相、基体的取向关系为[110]β//[110]β1//[0001]α;■。展开更多
文摘为了研究Mg_(97)Gd_(2)Y_(1)合金中β'相的粗化过程以及相关析出结构的形成和演变机制,使用原子分辨的高角度环形暗场-扫描透射电子显微镜(high angle annular dark field scanning transmission electron microscope,HAADF-STEM)成像技术表征了合金不同时效阶段形成的析出结构,并结合第一性原理计算的方法分析了它们的稳定性.结果表明,相关的β_(F)'、β_(M)和β″相主要在β'相粗化过程的早期形成,它们的形成与β'相相界面周围存在较高的错配应变场密切相关;随着β'相粗化过程的进行,β_(M)和β″相的尺寸和数量逐渐减少,而由β'与β_(F)'相交替组成的竹节状析出物增多,成为合金基体中主要的析出结构;当错配应变足够大时,β_(F)'相内部出现位错,β相在位错处可以形核,并逐渐长大成为基体中主要的平衡析出结构.
文摘采用聚焦离子束定点切割技术(Focused ion beam,FIB),透射电镜(Transmission electron microscopy,TEM)、高角度环形暗场扫描透射电镜(High angle annular dark field scanning transmission electron microscopy,HAADF-STEM)和扫描电镜(Scanning electron microscopy,SEM)等技术手段,对Mg-7Gd-5Y-1Nd-2Zn-0.5Zr合金铸态及(515℃,48 h)均匀化态的组织形貌进行观察分析。结果表明:铸态合金晶界共晶组织中含有(Mg,Zn)_(3)RE相(FCC,a=0.72 nm)、Mg_(5)(RE,Zn)相(FCC,a=2.24 nm)及块状长周期堆垛有序(Long-period stacking ordered,LPSO)相。其中LPSO相主要为18R结构,存在少量14H结构,局部区域存在少量不完整周期的LPSO结构;此外合金中存在分布于共晶相附近的微米级富RE相以及分布于晶粒内部的微米级富Zr颗粒。经过(515℃,48 h)均匀化热处理,晶界(Mg,Zn)_(3)RE相和Mg_(5)(RE,Zn)相完全回溶,残留相主要为14H-LPSO相,局部区域存在具有不同晶体结构的LPSO过渡相。在铸态合金的晶粒内部,沿[1120]_(a)晶带轴观察,发现存在几个原子面至纳米尺度的LPSO构建块,由不同数量的LPSO构建块单元(4个RE/Zn原子层)及Mg原子层交替堆垛构成,RE/Zn与Mg原子层堆垛次序不具备完整周期性;均匀化热处理后,晶内的LPSO构建块几乎回溶,仅剩下极少量单个LPSO构建块单元。沿[0001]_(a)晶带轴观察,晶粒内部存在多种分布方式的富RE/Zn原子柱,为Mg-Gd-Y系镁合金时效过程β′析出序列中GP区的早期结构。
基金the Natural Science Foundation of Jiangsu Province,China(No.BK20201035)the Talent Research Fund in Nanjing Institute of Technology,China(No.YKJ201957)+1 种基金the National Natural Science Foundation of China(Nos.51871035,52001159)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Nos.20KJB430016,20KJB430012).
文摘The effect of pre-straining on the structure and formation mechanism of precipitates in an Al−Mg−Si−Cu alloy was systematically investigated by atomic resolution high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM).Elongated and string-like precipitates are formed along the dislocations in the pre-strained Al−Mg−Si−Cu alloy.The precipitates formed along the dislocations exhibit three features:non-periodic atomic arrangement within the precipitate;Cu segregation occurring at the precipitate/α(Al)interface;different orientations presented in one individual precipitate.Four different formation mechanisms of these heterogeneous precipitates were proposed as follows:elongated precipitates are formed independently in the dislocation;string-like precipitates are formed directly along the dislocations;different precipitates encounter to form string-like precipitates;precipitates are connected by other phases or solute enrichment regions.These different formation mechanisms are responsible for forming different atomic structures and morphologies of precipitates.
基金Project(2014CB644000)supported by the National Basic Research Program of ChinaProject(2016YFB0701301)supported by the National Key Technology R&D Program of China+1 种基金Projects(51371200,51671218)supported by the National Natural Science Foundation of ChinaProject supported by State Key Laboratory of Powder Metallurgy,Central South University,China
文摘A combinatorial approach was applied to investigating the influence of Fe content on the microstructures and properties of Ti6Al4V alloy.A diffusion couple was manufactured with Ti6Al4V and Ti6Al4V20Fe alloys and annealed at 1000°C for 600 h to obtain a wide range of compositions.By combining electron probe micro-analysis(EPMA),scanning electron microscopy(SEM)and nanoindentation,the relationships between composition and microstructure as well as hardness were determined.It is found that after aging the Ti6Al4V5Fe sample contains reasonable(about 55%)volume fraction of fineαphase and shows the peak hardness among the Ti6Al4VxFe alloys.Therefore,it is a promising candidate for the development of titanium alloys.HAADF-STEM and XRD reveal that after quenching from the singleβphase field,the metastableα''lamellae form in the Ti6Al4V5Fe alloy,and on subsequent isothermal aging,theα''lamellae become coarse and act as precursors/preferential nucleation sites for the stableαphase.
基金Projects(51871195,51501015)supported by the National Natural Science Foundation of ChinaProject(TC170A5SU-1)supported by Ministry of Industry and Information Technology of China。
文摘The morphology and crystal structure of the precipitates in Mg-7Gd-3Y-1Nd-1Zn-0.5Zr(wt.%)alloy with fine plate-like 14H-LPSO structures aged at 240℃were investigated using transmission electron microscopy(TEM)and high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM).Fine plate-like 14H-LPSO structures precipitate after heat treatment at 500℃for 2 h,andβ-type phases precipitate after the alloy is aged at 240℃.The long-period atomic stacking sequence of 14H-LPSO structures along the[0001]αdirection is ABABCACACACBABA.After being aged at 240℃for 2 h,theβ-type phases are the ordered solution clusters,zig-zag GP zones,and a small number ofβ′phases.The peak hardness is obtained at 240℃for 18 h with a Brinell hardness of 112,theβ-type phases areβ’phases and local RE-rich structures.After being aged at 240℃for 100 h,theβ-type phases areβ’,β1 andβ’F phases.β′phases nucleate from the zig-zag GP zones directly withoutβ″phases,and then transform intoβ1 phase byβ’→β’F→β1 transformations.The Zn not only can form LPSO structure,but also is the constituent element ofβ1 phases.LPSO structures have a certain hindrance to the coarsening ofβ’andβ1 along<0001>α.
基金Project supported by the ITER-National Magnetic Confinement Fusion Program(Grant Nos.2010GB109000,2011GB108009,and 2014GB123000)the National Natural Science Foundation of China(Grant No.11075119)
文摘Solid helium bubbles were directly observed in the helium ion implanted tungsten(W), by different transmission electron microscopy(TEM) techniques at room temperature. The diameters of these solid helium bubbles range from1 nm to 8 nm in diameter with the mean bubble size about 3 nm. The selected area electron diffraction(SAED) and fast Fourier transform(FFT) images revealed that solid helium bubbles possess body-centered cubic(bcc) structure with a lattice constant of 0.447 nm. High-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)images further confirmed the existence of helium bubble in tungsten. The present findings provide an atomic level view of the microstructure evolution of helium in the materials, and revealed the existence of solid helium bubbles in materials.
文摘本论文使用球差校正的高角环形暗场扫描透射电镜(Aberration-Corrected High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy,HAADF-STEM)结合选区电子衍射(Selected Area Electron Diffraction,SAED)技术系统表征了Mg-19.6 wt.%Gd合金300℃等温时效100 h后的时效析出行为。研究结果表明,Mg-19.6 Gd合金时效后期析出的平衡相为β-Mg5Gd。β-Mg5Gd相为fcc结构(空间群:■;晶格参数:a=22.34?),呈透镜状。β-Mg5Gd相具有一个■的惯习面,它们沿■3个方向均匀分布。β-Mg5Gd相在β1-Mg3Gd中形核,并由内而外生长取代β1相。β相与β1,以及与α-Mg基体都是完全共格的,其与β1相、基体的取向关系为[110]β//[110]β1//[0001]α;■。